1. Field of the Invention
Specifically, the invention relates to a modulating apparatus and a demodulating apparatus. This invention relates to a spread spectrum modulating apparatus and a spread spectrum demodulating apparatus.
2. Description of the Prior Art
In some conventional spread spectrum communication systems, a transmitter includes primary and secondary modulators. The primary modulator modulates a carrier with an information signal and thereby derives a primary modulation signal. In general, the modulation executed by the primary modulator is of the FM (frequency modulation) type, the FSK (frequency shift keying) type, or the PSK (phase shift keying) type. The secondary modulator modulates the primary modulation signal with a spread code and thereby derives a secondary modulation signal (a spread spectrum signal). The spread spectrum signal is transmitted from the transmitter to a receiver of the conventional communication systems. The receiver includes a spread code generator producing a spread code which corresponds to the spread code used in the transmitter. The receiver also includes a despreading circuit which despreads the spread spectrum signal with the spread code to recover a primary modulation signal from the spread spectrum signal. The despreading circuit is a demodulator having a function inverse with respect to the function of the secondary modulator in the transmitter. The receiver further includes a second demodulator which recovers an information signal from the primary modulation signal. The second demodulator has a function inverse with respect to the function of the primary modulator in the transmitter.